FLAP is a key initiator of the leukotriene synthesis pathway that binds and then transfers arachidonic acid to 5-lipoxygenase (M. Abramovitz et al., “5-lipoxygenase-activating protein stimulates the utilization of arachidonic acid by 5-lipoxygenase,” Eur. J. Biochem., 1993, 215, 105-11). FLAP has been demonstrated to interact with LTC4 synthase, and could putatively modulate the production of LTC4 (T. Strid et al., “Distinct parts of leukotriene C(4) synthase interact with 5-lipoxygenase and 5-lipoxygenase activating protein,” Biochem. Biophys. Res. Comm., 2009, 381(4), 518-22). Modulation (including without limitation inhibition) or genetic deletion of FLAP blocks leukotriene production, specifically LTB4, the cysteinyl leukotrienes (LTC4, LTD4 and LTE4) as well as 5-oxo-ETE (J. Z. Haeggström et al., “Lipoxygenase and leukotriene pathways: biochemistry, biology, and roles in disease,” Chem Rev., 2011, 111(10), 5866-98).
Leukotrienes are immune-modulating lipids formed from arachidonic acid (reviewed in B. Samuelsson, “Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation,” Science, 1983, 220, 568-75). They are synthesized primarily by eosinophils, neutrophils, mast cells, basophils, dendritic cells, macrophages and monocytes. Leukotrienes mediate multiple biological effects including, by way of example only, smooth muscle contraction, leukocyte recruitment and activation, cytokine secretion, fibrosis, mucous secretion, and vascular function (J. Z. Haeggström, at 5866-98).
FLAP-deficient mice are healthy and reproduce normally. They do not produce leukotrienes and have decreased susceptibility in mouse models of arthritis (R. J. Griffiths et al., “Collagen-induced arthritis is reduced in 5-lipoxygenase-activating protein-deficient mice,” J. Exp. Med., 1997, 185, 1123-29). In humans, FLAP itself has been linked by genetic studies to respiratory disorders and cardiovascular disease, including myocardial infarction, atherosclerosis and stroke (A. Helgadottir et al., “The gene encoding 5-lipoxygenase activating protein confers risk of myocardial infarction, atherosclerosis and stroke,” Nat. Genet., 2004, 36, 233-39; A. S. Tulah et al., “The role of ALOX5AP, LTA4H and LTB4R polymorphisms in determining baseline lung function and COPD susceptibility in UK smokers,” BMC Med. Genet., 2011, 29(12), 173; R. Ji et al., “Genetic variants in the promoter region of the ALOX5AP gene and susceptibility of ischemic stroke,” Cerebrovasc. Dis., 2011, 32(3), 261-68; J. W. Holloway et al., “The role of LTA4H and ALOX5AP polymorphism in asthma and allergy susceptibility,” Allergy, 2008, 63(8), 1046-53). In addition, studies using animal models support a causative role for leukotrienes in aortic aneurisms, atherosclerosis, myocardial infarction, atherosclerosis, and stroke (reviewed in J. Z. Haeggström, at 5866-98).
Leukotrienes also play a role in autoimmune disorders such as rheumatoid arthritis, inflammatory bowel disease, nephritis, spondyloarthritis, polymyositis, dermatomyositis, gouty effusions, systemic lupus erythematosus, systemic sclerosis, Alzheimer's disease and multiple sclerosis (S. Chwiéko-Minarowska et al., “The role of leukotrienes in the pathogenesis of systemic sclerosis,” Folia Histochem. Cytobiol., 2012, 50(2), 180-85; M. Rosnowska et al., “Leukotrienes C4 and B4 in cerebrospinal fluid of patients with multiple sclerosis,” Pol. Merkuriusz Lek., 1997, 2, 254-55; and reviewed in J. Z. Haeggström, at 5866-98; I. Loell et al., “Activated LTB4 pathway in muscle tissue of patients with polymyositis or dermatomyositis,” Ann. Rheum. Dis., 2013, 72(2), 293-99; J. Chu et al., “Involvement of 5-lipoxygenase activating protein in the amyloidotic phenotype of an Alzheimer's disease mouse model,” J. Neuroinflammation, 2012, 9, 127). Leukotrienes have also been implicated in several aspects of carcinogenesis including tumor cell proliferation, differentiation, and apoptosis, tumor-associated angiogenesis, as well as the migration and invasion of carcinoma cells (D. Wang and R. N. Dubois, “Eicosanoids and cancer,” Nat. Rev. Cancer, 2010, 10(3), 181-93).
Leukotrienes play a key role in allergic disorders such as allergic rhinitis, allergic dermatitis and asthma, as well as respiratory disorders such as exacerbations, non-allergic asthma, fibrotic lung diseases, acute respiratory distress syndrome and chronic obstructive pulmonary disease (reviewed in J. Z. Haeggström at 5866-98). Approved antagonists of the LTC4 receptor and leukotriene synthesis modulators such as zileuton have shown clinical efficacy in a variety of respiratory disorders (reviewed in M. E. Krawiec and S. E. Wenzel, “Leukotriene modulators and non-steroidal therapies in the treatment of asthma,” Expert. Opin. Pharmacotherapy, 2001, 2(1), 47-65).
All the above evidence supports a key role of leukotrienes in a variety of human diseases and/or disorders, and FLAP modulation would be effective for the prevention, treatment, or amelioration of these immune-mediated inflammatory diseases and/or disorders. Furthermore, there still remains a need for FLAP modulator compounds that have pharmacokinetic and pharmacodynamic properties suitable for use as human pharmaceuticals.